Anisotropic spinning solutions from aromatic polyamides have been described in Kwolek U.S. Pat. No. 3,671,542 and in U.S. Pat. No. Re. 30,352. These solutions (dopes) are useful in making aramid fibers of very high tenacity and modulus.
More recently optically anisotropic solutions of cellulosic materials have been described in French Pat. No. 2,340,344, and these too have provided high tenacity/high modulus fibers. The ever-increasing costs of petrochemicals gives increasing impetus to the study of fibers from renewable sources, such as the cellulosics. In particular cellulosic fibers with properties approaching the aramid properties have been sought. Considerable effort has been applied to the use of optically anisotropic solutions to obtain the desired properties, but heretofore this effort has not been successful in providing cellulosic fiber property levels beyond about 6.8 dN/tex tenacity for cellulose triacetate or about 9.6 dN/tex tenacity for regenerated cellulose, both as described in Example 6 of French Pat. No. 2,340,344.
In the cellulose textile field it has been proposed that higher DP (degree of polymerization) should provide improved properties in the resulting fibers or films but it has not been possible to accomplish this goal because of the extremely high viscosity of the solutions. Anisotropic solutions provide the opportunity for spinning at high concentrations without excessive viscosities, but prior to the present invention adequate solvents for forming high concentration solutions of high DP cellulose triacetate have not been available.